Security services were last night studying our dossier on his drive to recruit fanatics in the UK over the internet.

He said in an email: "The options that you have for operations could be pipe bombs, assassinations or using a firearm at a location crowded with enemies."

The last suggestion is a clear reference to the Mumbai massacre in which 164 people were killed when terrorist gunmen went on the rampage in the Indian city in 2008.

The Sun contacted warlord Awlaki - widely tipped to become al-Qaeda's global leader following the killing of Osama Bin Laden - in an email sting.

It confirmed the threat he poses to innocent British citizens. It showed the ease with which a determined extremist can link up with him.

And it provided a grim insight into how al-Qaeda can recruit disciples through the internet.

Awlaki, 40, has already engineered a string of attempted outrages here and in the US.

He brainwashed 21-year-old student Roshonara Choudhry into stabbing Labour MP Stephen Timms over his support for the war in Iraq.

And he urged British Airways computer worker Rajib Karim, 31 - now in jail - to assist in a plot to blow up an airliner in a Lockerbie-style attack.

born cleric Awlaki, dubbed the Bin Laden of the internet because he uses the web to spread his evil gospel, was also behind last year's ink bomb plot to down cargo jets.

The Sun's sting worked like this:

FIRST, we obtained an email address for Awlaki's Yemen-based "al-Qaeda in the Arabian Peninsula" network hidden in material on an extremist website.

then our investigator, posing as a UK-based fanatic named "Q. Khan," sent an email addressed personally to Sheikh Anwar al-Awlaki. FINALLY, we received a reply from the terror chief - convinced he was in contact with the leader of a British cell eager to obey his commands. Our man "Khan" wrote:

Sheikh Anwar, the brothers and I need some help with a query about the pipe devices. We've had enough of talking and want to take things into our own hands as regards the situation towards the haters of the Prophet.

A lot of us are suspicious about some goings on at the local masjid (mosque) and a potential Scotland Yard informer.

We are resolved to go it alone. Should we be planning to go all at once, or should one follow the other in a series of operations? Your advice will be most graciously received.

Awlaki's reply appeared to have been drafted three days later but took weeks to reach us after it was filtered through his encryption system. He said in English:

We ask Allah to give you the strength and steadfastness to serve His religion. If you are a group of brothers who trust each other then you may work together. Otherwise we advise you to work alone. In case you decide to work together then it is definitely better to go all at once.

options that you have for operations could be pipe bombs, assassinations or using a firearm at a location crowded with enemies.

We would also suggest that if you have decided to go ahead do not contact us because this may bring surveillance on you.

However, right before you start your operation you may send us a message informing us of the operation without mentioning the details. This is of course if you want us to sponsor the operation.

The message was signed: "Your brothers at al-Qaeda of the Arabian Peninsula."

In another email, our investigator posed as a British woman named Catherine Nelson who had been converted to radical Islam.

"Catherine" said she worked in a government department in London and asked Awlaki to "advise how I might serve and start following the right path".

this time Awlaki's response was more circumspect.

After greeting "Sister Catherine," he said: "We ask Allah to reward you and grant you the best in this world and the next.

"To answer your query about how to serve the religion, the avenues to do so are many.

"We are not stating any specific suggestions here because only you would know the best way to serve based on your circumstances." The Sun has passed our dossier on the email sting to the security services.

And last night a British intelligence source warned: "There is no doubt this man now clearly represents a very grave danger."

Britain, the US and allies are braced for revenge attacks following the killing of Bin Laden.

And repeating the Mumbai slaughter in a European city is one of al-Qaeda's top priorities.

Tory MP Patrick Mercer said of our probe: "I have no doubt the Home Office will want to investigate how simple it is to get in touch with Awlaki and his people.

"He is a leading contender to fill the power vacuum left by Osama Bin Laden